COLOUR Cemre Ünal 12-C

Food Colour The color of food is due to the ability of substances in the food to absorb light in the visible region of the electromagnetic spectrum. The substances that cause food to be colored may be natural (pigments) or synthetic (dyes).

PIGMENTS Anthocyanins Carotenoids Chlorophyll Haem

Anthocyanins Most widely occuring in pigmets in PLANTS. Responsible for pink, red, purple and blue colors in fruits and vegetables.

Carotenoids Most widespread pigments in nature (mostly produced by algae) Acts as a precursor for VITAMIN A synthesis Colors range from yellow-red/orange. Red astaxanthin (complexed to a protein) is responsible for the blue green color of live crabs and pink color on salmon.

Chlorophyll Major pigmets necessary for photosynthesis found in green plants. Haem Myoglobin is responsible for the purple-red color of fresh meat.

Synthetic Colorants (DYES) They are the artificial ingredients that provide color and flavour. Any artificial dyes used in the past have been shown to be potentially carcinogenic.

Analyzing Color From Spectra In a visible spectrometer the amount of light absorbed is measured again the wavelength of the light passing through the sample to provide an absorption spectrum. This can be illustrated with the visible spectro of chlorophyll.

Spectrum of Chlorophyll a and Chlorophyll b

Factors Affecting the Color Stability of Pigments Any factor which will change the structure of the molecule will affect the color as this will affect the precise wavelength of visible light that pigment absorbs. Oxidation Temperature Change pH Change Presence of Metal Ions

ANTHOCYANINS Anthocyanins exist in different forms. In aqueous solution these different forms are in equilibrium with each other. Changing the pH and the temperature affects the position of equilibrium. They are most highly colored at low temperatures and low pH (acidic solutions)

ANTHOCYANINS When exposed to heat the equilibrium moves to right and the compounds are less thermodynamically stable. This causes loss of color and browning. Anthocynanins also form complexes with metal ions such as aluminium ions, and iron (III) ions.

ANTHOCYANINS They contain the flavonoid skeleton

It is the conjugation of pi electrons contained in this structure which accounts for the color of anthocyanins. The more extensive the conjugation, the lower energy of the light absorbed. This can be explained by using cyanidin.

In acidic solution it forms a positive ion and there is less conjugation than in alkaline solution where pi electrons in the extra bond between the carbon and oxygen are also delocalized. Structure of Cyanidin in acidic solution. Less Conjugation so absorbs blue-green region and transmits red light. Structure of cyanidin in alkaline solution More conjugation so absorbs in the orange region of the spectrum and transmits blue light.

Other anthocyanins differ in the number and types of other groups such as hydroxyl or methoxy groups which affects the precise wavelength of the light. The basic flavonoid is essentially non-polar. As more polar hydroxyl groups are added the potential for them to form hydrogen bonds with water molecules increases and many anthocyanins are soluble in water.

CAROTENOIDS They contain many alternate C-C , or C═C bonds. Because of unsaturation due to the C═C bonds caretenoids susceptible to oxidation. Oxidation process can be catalyzed by light, metals and hyroperoxides. This changes the type of bonding and results in the bleaching of color.

Carotenoids are stable up to 50˚C and in a pH range of 2-7. When heated the naturally occuring tran-isomer rearreanges to the cis-isomer.

In carotenoids the conjuction is mainly due to a long hydrocarbon chain (as opposed to anthocyanins) consisting of alternate single and double C-C bonds. The majority are derivered from a (poly)ene chain containing forty carbon atoms which may be terminatedby cyclic end groups and may also be complemented with oxygen containing functional groups. Alfa, Beta-carotene and vitamin A are all fat soluble and not water soluble.

CHLOROPHYLL Different forms of chlorophyll contain different groups attached in the R-position Chlorophyll contains a group with four nitrogen atoms which is called a porphin.

The porphin ring forms a very stable complex with a magnesium ion with the non-bonding electrons on the nitrogen atoms.

In a basic solution with a pH of 9 it is thermodynamically stable but in acidic solution with a pH of 3 is unstable. When heated, the cell membrane of the plant deteriorates releasing acids which decrease the pH. At this lower pH magnesium ion is replaced by two hydrogen ionsresulting in the formation of an olive-brown pheophytin complex

HAEM (HEME) The haem group also contains a porphin ring but it is complexed to an iron ion. During oxidation, oxygen binds to pruple-red oxyoglobin(Mb) and red oxymyoglobin forms. In both the iron group is in the form of iron (II). Through auto-oxidation of Mb and red oxymyoglobin the oxidation state of ıron is changed into iron (III). This state is called metmyoglobin.

In order to minimize the rate of auto-oxidation meat can be stored free of oxygen.

Chlorophyll and Haem They both contain a planar heterocyclic unit with the general name of porphin. Porphins contain a cyclic system in which all the carbon atoms are in sp2 hybridized. This results in a planar structure with extensive pi conjugation.

Porphin groups have 1-8 different positions. In chlorophyll the porphin complex with the original double bond between positions 7 and 8 is now saturated. In chlorophyll a the –R group is methyl group and in chlorophyll b the r group is an aldehyde group.

HAEM Heamoglobin is the oxygen carrier in the blood of mammals and myoglobin is the primary pigment in muscle tissue and is a complex of protein, globin, together with a haem group which is porphin ring containing iron (II) as a central atom. The haem group is present both in myoglobin and heamoglobin.

NON ENZYMATIC BROWNING OF FOOD Food high in carbohydrate content, esp. Sucrose and reducing sugars, lacking nitrogen-containing compounds can be caramelized. Both molecules sucrose and glucose when caramelized form many different products, sweet and bitter derivatives of acids.

CARAMELIZATION For acids lower than pH < 3 and for bases pH > 9. Factors that increase the rate of caramelization include the pH change and the temperature. For acids lower than pH < 3 and for bases pH > 9. Temperature above 120 celcius degrees is required.

MAILLARD REACTION For foods contain nitrogen Maillard Rxn occurs. This involves the reaction of a carbohydrate, either a free sugar or one bound up in starch, with the amine group on an amino acid, which may also be a part of a protein chain.

MAILLARD RXN Basicly it involves a condensation rxn between the carbonyl group on the reducing sugar and the amine group. The presence of amino acid lysine results in the most browning color and cytesine the least.

Some of the foods contain lysine readily. Moisture lowers the temperature, in order to make a good stew it is sensible to brown the meat.